Though it has been known that color vision is mediated by three types of photoreceptors for some 200 years, there is little information about how the spacing and packing geometry of the short (S), middle (M), and long (L) wavelength sensitive cones. The spatial organization of the S cones is the best known, while almost nothing is known about M and L cone distribution. Even the ratio of L to M cones has proven elusive. The goal of this proposal is to determine the spacing and packing geometry of these three interleaved cone submosaics in the primate retina. In order to resolve individual photoreceptors using the light returned following a double pass through foveal cones: 1) A patch of retina will be removed from the eye and maintained in vitro. 2) Water immersion optics will be used to image the photoreceptor mosaic on a high resolution, high sensitivity CCD camera. The camera takes advantage of recent advances in low light imaging borrowed from astronomy. By comparing the amount of light reflected from the retina at three wavelengths chosen to produce the highest contrast between the cone types, first with the photopigment unbleached and then again following bleaching, the type of photopigment contained by each cone will be determined. The resulting maps showing the organization of the three types of photoreceptors across the retina will make it possible to 1) study how trichromacy is incorporated into the retina with minimal cost for spatial vision, 2) explore the contributions of the three cone types to the post- receptoral channels that are known from psychophysical experiments, 3) determine the chromatic organization of retinal receptive fields as a first step towards understanding the retinal circuitry that implements chromatic opponency, and 4) determine whether there are mechanisms responsible for forming regular patterns of cones during development.